It is generally known that platinum catalysts will accelerate the addition of compounds containing silicon bonded hydrogen atoms to compounds containing aliphatic unsaturation. In U.S. Pat. No. 3,419,593, Willing discloses that virtually any compound which contains an .tbd.SiH group can be reacted with practically any compound which contains aliphatic multiple bonds in the presence of a platinum compound such as chloroplatinic acid. Also, it is shown for example, in U.S. Pat. No. 3,814,730 to Karstedt that compounds containing silicon hydrogen atoms can be added to organopolysiloxanes containing aliphatic multiple bonds and having at least 50 silicon atoms per molecule at room temperature.
Although the known platinum catalysts will substantially increase the cure rate of organopolysiloxane compositions, the "pot-life" or working time is also substantially reduced. Thus it would be desirable to provide a means for controlling the rate at which a platinum induced addition reaction of Si-bonded hydrogen atoms to an organopolysiloxane containing aliphatic unsaturation and having 50 silicon atoms per molecule can occur at room temperature so that a constant and predetermined rate of reaction can be obtained. This would provide adequate time between the preparation of the mixture and crosslinking, even though crosslinking occurs at temperatures below 40.degree. C up to room temperature. Control of the reaction rate is of particular importance with respect to dental impression compounds consisting of diorganopolysiloxanes having terminal triorganosiloxy groups in which at least one terminal organic group is a vinyl group, organopolysiloxanes containing at least 3 Si-bonded hydrogen atoms per molecule, a platinum catalyst and other compounds such as fillers, if desired. Heretofore, it was necessary to prepare or obtain copolymers having vinyl groups in the diorganosiloxane units such as disclosed in U.S. Pat. No. 3,699,073 to Wada et al.
Therefore it is an object of this invention to provide a process for controlling the rate of addition of silicon bonded hydrogen atoms to compounds having aliphatic unsaturation. Another object of this invention is to provide a process for preparing organopolysiloxane compositions having a longer "pot-life" or working time. A further object of this invention is to provide a process for preparing organopolysiloxane compositions having a controlled rate of addition of silicon bonded hydrogen atoms to an organopolysiloxane containing aliphatic unsaturation and having at least 50 silicon atoms.